Scalable Vector Graphics (SVG) is an Extensible Markup Language (XML) based language for representation of static and dynamic vector graphics. SVG is vector-based which means that the content is not made for certain screen resolutions but can be easily scaled. SVG is standardized by the World Wide Web Consortium (W3C). The mobile profile of SVG version 1.1 was adopted by 3GPP Release 5 and it is today supported by roughly 100 million mobile handsets.
SVG Tiny 1.2 [1] is a more powerful version of SVG that is specifically designed for mobile devices and terminals. It is currently a W3C candidate recommendation and has been adopted by 3GPP Release 6. Support for a variety of new multimedia features, including full control of audio and video, is included along with micro Document Object Model (μDOM) and scripting.
In addition to being a media type for vector graphics, SVG can also be used as a scene description language, where a scene can be composed temporally as well as spatially. In fact, SVG Tiny 1.2 is currently under consideration as the presentation format for the 3GPP work item on Dynamic and Interactive Multimedia Scenes (DIMS) as well as for the Open Mobile Alliance (OMA) work item on Rich-Media Environment (RME). The standardization of DIMS and RME are currently active and it is expected that the work items will produce aligned deliveries. For DIMS (and also for RME), the main competing proposals are the Mobile Open Rich media Environment (MORE) [2] building on technologies from W3C and the Lightweight Application Scene Representation (LASeR) [3] standardized by MPEG. Both use SVG Tiny 1.2 as basis.
DIMS (RME) content, as opposed to pure SVG content, can be streamed using the Real-time Transport Protocol (RTP) [4]. The rendered SVG document is referred to as an SVG scene and will typically be updated with smaller scene updates. MORE and LASeR specify how SVG scenes can be transported over RTP. The mechanisms for scene updates are conceptually similar, albeit not identical. LASeR specifies its own mechanisms, whereas MORE uses Remote Events for XML (REX) [5] by W3C.
The ability to recover from errors is essential, especially when unreliable protocols such as RTP are used. Random Access Points (RAPs) are defined in both the MORE and LASeR proposals for this purpose. When an error occurs, one must wait for the next RAP to recover. This RAP is decoded the same way as if one was tuning in for the first time. Everything from the old scene is deleted, and a new tune-in is performed.
The prior art technique of using a RAP to recover from an error is a way of discarding all data and starting again from scratch. All media from before the RAP is destroyed and reinitialized, and all interactivity is lost. This means that even a small error will cause a complete re-initialization of the client.
In order to rely on recovery by using RAPs, it is also necessary to include RAPs frequently in the bit stream. As RAPs typically are large compared to differential scene information, there will be a substantial overhead of redundant data.
Complete re-initialization of a client causes a severe negative impact on user experience. A pause in the audio and video is almost inevitable and the client will revert to default settings.